Epoxy resin is considered as the most cost-effective binder for anti-corrosion coating due to its excellent adhesion to metal, mechanical rigidity and chemical resistance properties. Epoxy primers are usually overcoated by a variety of topcoats, including solvent or water based epoxy, acrylate, polyurethane, polysiloxanes or other functional finishes.
There is an optimum time for epoxy to be overcoated, within this period no additional surface preparation is required. After the “overcoat window” has passed, the primer will need to be abraded before it can be topcoated, which is an expensive and labor-consuming process.
Overcoat window varies in each system according to the specific material and conditions applied. Temperature has significant influence on the overcoat window. 7 to 14 days are the typical overcoat window in most cases. Overcoating beyond the overcoat window will lead to weak intercoat adhesion and even paint failure, which causes significant scheduling issues or rework in the industry hampering throughput.
It is therefore, still interesting in the art to develop a coating having balanced overcoat window time and anti-corrosion properties.